1. Field of the Invention
The present invention relates generally to medical devices and, more particularly, to sensors used for sensing physiological parameters of a patient.
2. Description of the Related Art
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
In the field of medicine, doctors often desire to monitor certain physiological characteristics of their patients. Accordingly, a wide variety of devices have been developed for monitoring many such characteristics of a patient. Such devices provide doctors and other healthcare personnel with the information they need to provide the best possible healthcare for their patients. As a result, such monitoring devices have become an indispensable part of modern medicine.
One technique for monitoring certain physiological characteristics of a patient is commonly referred to as pulse oximetry, and the devices built based upon pulse oximetry techniques are commonly referred to as pulse oximeters. Pulse oximetry may be used to measure various blood flow characteristics, such as the blood-oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the tissue, and/or the rate of blood pulsations corresponding to each heartbeat of a patient. In fact, the “pulse” in pulse oximetry refers to the time varying amount of arterial blood in the tissue during each cardiac cycle.
Pulse oximeters typically utilize a non-invasive sensor that transmits electromagnetic radiation, such as light, through a patient's tissue and that photoelectrically detects the absorption and scattering of the transmitted light in such tissue. One or more of the above physiological characteristics may then be calculated based upon the amount of light absorbed and scattered. More specifically, the light passed through the tissue is typically selected to be of one or more wavelengths that may be absorbed and scattered by the blood in an amount correlative to the amount of the blood constituent present in the tissue. The measured amount of light absorbed and scattered may then be used to estimate the amount of blood constituent in the tissue using various algorithms.
Pulse oximetry readings measure the pulsatile, dynamic changes in amount and type of blood constituents in tissue. Other events besides the pulsing of arterial blood may lead to modulation of the light path, direction, and the amount of light detected by the sensor, creating error in these measurements. Pulse oximetry is sensitive to movement, and various types of motion may cause artifacts that may obscure the blood constituent signal. For example, motion artifacts may be caused by moving a sensor in relation to the tissue, by increasing or decreasing the physical distance between emitters and detectors in a sensor, by changing the direction of emitters or detectors with respect to tissue or each other, by changing the angles of incidence and interfaces probed by the light, by directing the optical path through different amounts or types of tissue, or by expanding, compressing or otherwise altering tissue near a sensor. In the emergency room, critical care, intensive care, and trauma center settings, where pulse oximetry is commonly used for patient monitoring, the wide variety of sources of motion artifacts includes moving of a patient or the sensor by healthcare workers, physical motion of an unanaesthetised or ambulatory patient, shivering, seizures, agitation, response to pain and loss of neural control. These motions oftentimes have similar frequency content to the pulse, and may lead to similar or even larger optical modulations than the pulse.
Two categories of pulse oximetry sensors in common use may be classified by their pattern of use: the disposable and the reusable sensor. Disposable sensors are typically flexible bandage-type structures that may be attached to the patient with adhesive materials, providing a contact between the patient's skin and the sensor components. Disposable sensors have multiple advantages, including ease of conformation to the patient. The flexible nature of disposable sensors further renders them susceptible to motion artifacts caused by mechanical deformation of the sensor, which changes the amount of light detected. Reusable sensors, often semi-rigid or rigid clip-type devices, are also vulnerable to motion artifacts, such as artifacts caused by partial opening of the clip in response to patient motion. Both categories of sensors may have modulations of detected light induced by the physical motion of the sensor components with respect to each other and the tissue.
Motion artifacts may sometimes be addressed by signal processing and filtering to mitigate the effects of motion after the motion has occurred. However, it would be desirable to provide a sensor that reduces the occurrence of movement that may lead to motion artifacts.